An ultrasound system has become an important and popular diagnostic tool since it has a wide range of applications. Specifically, due to its non-invasive and non-destructive nature, the ultrasound system has been extensively used in the medical profession. Modern high-performance ultrasound systems and techniques are commonly used to produce two or three-dimensional images of internal features of an object (e.g., human organs).
Generally, the ultrasound image is displayed in a Brightness-mode (B-mode) by using reflectivity caused by an acoustic impedance difference between the tissues of the target object. However, if the reflectivity of the target object is hardly different from those of the neighboring tissues such as tumor, cancer or the like, then it is not easy to recognize the target object in the B-mode image.
To cope with the problem of recognizing the tumor, cancer and the like in the B-mode, an ultrasound elasticity imaging has been developed to visualize the mechanical characteristics of the tissues based on differences responsive to pre-compression and post-compression. Such imaging proved very helpful for diagnosing lesions such as tumor and cancer, which otherwise are hardly recognized in the B-mode image, in soft tissues (e.g., breast). The ultrasound elasticity imaging may utilize the scientific property that the elasticity of the tissues is related to a pathological phenomenon. For example, the tumor or cancer is relatively stiffer than the surrounding normal tissues. Thus, when stress is uniformly applied, a strain of the tumor or cancer may be typically smaller than those of the surrounding tissues. Strain refers to deformation of a target object due to stress applied per area and Young's modulus may be defined as a ratio of stress over strain.
Generally, if the stress is applied to a target object, then tissues in the target object may be compressed in an axial direction and moved out in a lateral direction. The conventional ultrasound elasticity imaging may use only the displacements in an axial direction to form a strain image without considering the movement in a lateral direction. Thus, there is a problem that an accurate strain image may not be formed due to a calculation error of the displacements.